Aldehydes, particularly linear paraffinic aldehydes, are extremely useful as intermediates in organic synthesis because of their terminal carbonyl group which is among the most active groupings in organic compounds. For instance, they are easily reduced and oxidized and take part in a number of addition reactions. More specifically, paraffinic (alkyl) aldehydes are readily catalytically reduced to the primary alcohols, and oxidized to the corresponding carboxylic acids. They also undergo addition and/or condensation reactions with hydrogen cyanide, alcohols, nitroparaffins as well as condensations with themselves and other carbonyl-containing compounds. Further, these aldehydes condense with ammonia and its derivatives including primary amines. The latter condensation products (which are commonly known as Schiff bases) lend themselves to applications as surfactants or detergents when solubilized by processes such as sulfation or oxyalkylation.
In the aforementioned pending application the applicants disclosed novel three component, ligand stabilized, homogeneous hydroformylation catalysts consisting essentially of (1) platinum(II) dihalides, stabilized with (2) one or more Group VB, VIB or VIIB donor ligands and used in combination with (3) Group IVB metal halide co-catalysts.
It has now been demonstrated that under relatively mild reaction parameters some of these homogeneous catalysts have the unexpected ability to preferentially and selectively hydroformylate alpha-olefins contained in alpha-olefin-internal olefin mixtures to the substantial exclusion of hydroformylating the internal olefins in the mixture. That is, as long as the mixture of olefins contains a substantial quantity of alpha (or 1-) olefins in addition to internal (non-terminal) olefins, preferential hydroformylation of the alpha olefin takes place until 80-95% conversion of the alpha-olefin fraction is converted to the linear aldehyde containing 1 more carbon atom than the original 1-olefin.
This finding of selective and preferential hydroformylation is both surprising and unexpected since the hydroformylation of both alpha olefins alone and internal (non-terminal) olefins alone has been demonstrated in the aforementioned pending parent application using the novel three component platinum(II) hydroformylation catalysts of this invention.
In the broadest contemplated practice of this invention, selective and preferential hydroformylation of alpha-olefins in alpha-olefin-internal olefin mixtures containing a significant quantity of internal olefin takes place by: contacting the olefin mixture with at least a catalytic quantity of a three (3) component, ligand-stabilized, homogeneous platinum(II) catalyst complex consisting of (1) a platinum(II) dihalide, stabilized with (2) at least one Group VB donor ligand in combination with (3) a Group IVB metal halide co-catalyst, at elevated temperatures and superatmospheric conditions of pressure, with a gaseous mixture of hydrogen and carbon monoxide until about 80-95% of the alpha-olefins are selectively converted to linear aldehydes, and optionally separating the linear aldehydes contained therein.
In a preferred and more specific embodiment of the above-described process, essentially linear alkyl aldehyde products containing from 3 to 31 carbon atoms are prepared by the catalytic addition of hydrogen and carbon monoxide to an alpha-olefin-internal olefin mixture containing from about 10 to 90 mole % of internal olefins, said olefins containing 2 to 30 carbon atoms, by the process of:
a. admixing each mole of olefin contained in said mixture to be hydroformylated in a deoxygenated reaction media, with from 0.001 to 0.1 moles of a three component ligand-stabilized, homogeneous platinum(II) catalyst complex consisting essentially of (1) platinum(II) dihalide stabilized with (2) at least one Group VB donor ligand selected from the group consisting of trivalent phosphorus and trivalent arsenic bonded to one or more hydrocarbyl radicals, said radicals being selected from the group consisting of aryl, alkyl and substituted aryl radicals containing less than 20 carbon atoms, and (3) a tin(II) halide, said mole ratio of tin(II) halide to said ligand-stabilized platinum(II) dihalide complex ranging from 1/1 to 10/1, in the presence of sufficient inert solvent to disperse the components of the admixture, to form a deoxygenated reaction mixture.
b. pressurizing said reaction mixture to between about 100 psig to 3000 psig with at least sufficient carbon monoxide and hydrogen to satisfy the stoichiometry of the hydroformylation reaction referred to supra, said mole ratio of H.sub.2 :CO ranging from 30:1 to 1:30 moles of hydrogen for each mole of carbon monoxide;
c. heating said pressurized reaction mixture to temperatures between 25.degree. to 125.degree. C, until about 80 to about 95% of the alpha olefins contained in said olefin mixture is converted, then
d. isolating said linear aldehyde products contained therein.
In order to further aid in the understanding of this invention, the following additional disclosure is submitted.